Evaluation of Tensile Properties of Thermoplastic and Thermosetting Resins Using Small Samples with Small Punch Test

Abstract

The small punch test (SPT) is one of the micro test methods and uses small disc-shaped specimens of about ϕ3~10 mm x t0.5 mm. In this study, thermoplastic and thermosetting resins were targeted to expand the application of the SPT. The deformation behavior was verified and converted to tensile properties. 6-nylon (PA6), polyethylene terephthalate (PET), polycarbonate (PC), and polytetrafluoroethylene (PTFE) were used as thermoplastic resins, and epoxy and phenol as thermosetting resins. The load-displacement curves of all resins in the SP test were divided into 4 regions according to deformation behavior. Judging from the curve shapes, thermoplastic resins showed yielding behavior in the SP test, while thermosetting resins showed little yielding behavior. As for thermoplastic resins, the ordinates of the maximum load in the tensile test were significantly different from that in the SP test. In other words, it was confirmed that different properties were exhibited under uniaxial in tensile test and multiaxial stress in SP test. Regarding the failure modes, PET, PTFE, epoxy, and phenolic showed linear (radial) cracks from the center of the specimen, suggesting brittle failure. PA6 and PC exhibited circumferential cracks, suggesting ductile failure. In addition, the SPT results were converted to UTS and fracture ductility in tensile test. For 0.2% proof stress, good agreement between tensile and SP test results was obtained by using the same formula as for the metallic materials. For UTS, good agreement was obtained by excluding the effects of multiaxial stress fields. For fracture ductility, it was difficult to formulate a uniform formulation due to the effects of plastic instability regions and variations in resin material.